The present invention relates generally as indicated to a hydraulic motor and, more particularly, to a hydraulic motor with a gerotor drive assembly which provides rotational motion to a desired piece of machinery.
A hydraulic motor is a converter of pressurized oil flow into torque and speed for transferring rotational motion to a desired piece of machinery. A hydraulic motor will have a flow circuit which determines the path of fluid flow and which includes a working path and a non-working path. The working path extends between its inlet port and its outlet port, and the fluid passes therethrough to cause the drive assembly to rotate the output shaft in the appropriate direction. The non-working path includes chambers surrounding the drive train components (e.g., the drive link and the output shaft), and fluid passes therethrough for cooling and lubrication of these components. In a two-pressure-zone motor design, fluid traveling through the non-working path rejoins fluid traveling through the working path somewhere upstream of the outlet port. In a three-pressure-zone motor design, fluid traveling through the non-working path does not rejoin the working path and exits the motor through a separate case drain in the housing.
Of particular relevance to the present invention is a hydraulic motor wherein the pressure-to-rotation conversion is accomplished by a drive assembly having a gerotor set. A gerotor set comprises an outer stator and an inner rotor having different centers with a fixed eccentricity. The stator has internal xe2x80x9cteethxe2x80x9d or vanes which form circular arcs and the inner rotor has one less external xe2x80x9ctoothxe2x80x9d or lobe. The rotor lobes remain in contact with the circular arcs as the rotor moves relative to the stator and these continuous multi-location contacts create fluid pockets which sequentially expand and contract. As fluid is supplied and exhausted from the fluid pockets in a timed relationship, the rotor moves hypocycloidally (i.e., orbits and rotates) relative to the stator. A drive link is interconnected to the rotor for movement therewith, and this interconnection usually constitutes crowned external splines on the drive link which engage with internal splines on the rotor.
The drive link is interconnected to a shaft to transfer rotational movement thereto. For example, the motor can include a shaft, which is connected to the drive link (e.g., by a splined interconnection) and which can be coupled to the input shaft of the desired piece of machinery. Alternatively, the shaft can be part of the gearbox of the desired machinery and the drive link can be directly coupled thereto.
The drive assembly of a gerotor motor will typically include a valving system to supply and exhaust the fluid from the gerotor pockets in the desired timed relationship. One common type of valving system includes a spool valve which rotates with one of the drive train components (e.g., the output shaft or the drive link). A spool valve typically has a roughly cylindrical shape with inlets/outlets arranged about its outer circumferential surface so that it systematically opens and closes flow passages to and from the gerotor fluid pockets.
The spool valve can be located within the longitudinal bore of the motor""s front housing member and surrounded by a stationary manifold. Typically, the spool valve is integrated with the output shaft (e.g., formed in one piece therewith or tightly attached thereto) and rotates therewith during operation of the motor. Motors of this design are not expected to take on large side loads and/or high radial torque due to the potential for spool damage in the event of shaft deflection.
The spool valve can instead be located to the rear of the longitudinal bore and rotated with the drive link during operation of the motor. Specifically, for example, the spool valve can be positioned in a rear housing member (having manifold-like channels) positioned between the front housing member and the motor""s end cover. This design may minimize shaft-deflection issues, but it requires a substantial increase in the axial length, and thus package size, of the motor. While motor dimensions may not matter in some situations, they are crucial in many heavy duty applications.
Some of the most significant considerations when selecting a fluid motor, especially for heavy-duty applications, include the no-load pressure drop (or mechanical efficiency), life expectancy (e.g., service life), low speed performance, continuous operation condition, torque capacity, and side load limits. Accordingly, motor manufacturers are constantly trying to improve upon these performance parameters. Also, many heavy-duty motor applications are in environments with tight spacing tolerances, whereby package size (e.g., motor dimensions) can be as important as performance parameters. Furthermore, cost is almost always a concern, whereby economic considerations will usually always play a role in the development of a motor design.
The present invention provides a hydraulic motor comprising a front housing having a first port and a second port, a manifold, a spool valve, a drive link, and a shaft. The front housing and the manifold form a central bore in which the spool valve, the drive link and the shaft are rotatably mounted. The drive link transfers rotational motion to the shaft and the shaft is coupled to the spool valve so that rotational motion is transferred thereto. The coupling between the spool valve and the shaft includes a floating coupling element to prevent side loads on the shaft from being transferred to the spool valve. In this manner, the motor can take on large side loads and/or high radial torque while still positioning the spool valve in the front housing. This translates into a shorter package size and less working pressure drop.
The present invention also provides a sealing arrangement for rotating interfaces (e.g., the rotor and the end cover and/or a stationary component of the drive assembly), wherein the seal and the groove have a rotationally incompatible geometry. For example, the geometry can include a series of curved undulations, a series of corners, tabs, and/or notches which serve as rotation-preventing stops. The elimination of ring-rotation helps reduce interface friction, which can be especially significant during motor start-up as well as during continuous low speed operation of the motor, to thereby provide improved mechanical and hydraulic performance. Also, the minimization of interface friction in combination with the essential elimination of groove-to-seal friction (which results when a ring rotates within its groove) translates into longer seal life.
The present invention further provides a high pressure seal member wherein the outer lip has a length equal or greater than the length of the inner lip whereby the seal""s radially outer surface is equal or greater than its radially inner surface area. In this manner, the seal member is prevented from rotating with the shaft, thereby increasing the life of the seal (and thus the motor).
These and other features of the invention are fully described and particularly pointed out in the claims. The following description and drawings set forth in detail a certain illustrative embodiment of the invention, this embodiment being indicative of but one of the various ways in which the principles of the invention may be employed.